Positive effect of Mo on mechanical properties of a Ni-42W-10Co-xMo medium heavy alloy

In this study, a novel Ni-W-Co-Mo medium heavy alloy (MHA) was designed to improve its mechanical strength via Mo doping. In the Ni-42W-10Co-xMo alloy series, where x represents the weight percent of Mo and varies between 0, 1, 2, 5, and 10, the microstructure transitions from a dendritic structure to a hypoeutectic structure as the Mo content increases from 0 to 5wt.%. Moreover, as the Mo content increases from 0 to 10wt.%, the distribution of the μ-phase shifts from being individually dispersed to forming aggregates, and its volume fraction rises from 0.5% to 7.9%. Notably, the μ-phase evolves into an eutectic microstructure, which helps in minimizing the segregation of elements. This change is accompanied by a substantial enhancement in mechanical properties; specifically, the compressive yield strength at room temperature increases from 350 MPa to 646 MPa, indicating a significant 85% increase. Similarly, the microhardness increases from 230 HV to 304 HV. Molecular dynamics simulations further reveal that the strengthening mechanism of Ni-42W-10Co-xMo alloys is Mo-induced solid solution strengthening and precipitation strengthening.